Enabling Fast Mass Transport in Anode by a Smartly Built‐in LiC6 Phase for High‐Performance Solid‐State Lithium Metal Batteries

Abstract The practical use of solid‐state lithium metal batteries is hindered by the rapid growth of lithium dendrites through the solid electrolyte, leading to a short lifespan, and poor performance at high rates. The mass transport in anode bulk is proposed as a critical reason related to the chemo‐mechanical failure of the interface and growth of lithium dendrites. In this study, a lithium‐composite anode with a smartly integrated LiC 6 phase is developed using a thermodynamic reaction between molten Li and thermally expanded graphite. The gravity segregation effect creates a gradient dispersion of LiC 6 in Li, resulting in improved bulk Li diffusion kinetics (70 times higher than that of a pure Li anode). This composite electrode exhibits low interfacial resistance (≈2.3 Ω cm 2 ) and an ultra‐high critical current density of 2.4 mA cm −2 in all‐solid‐state symmetric cells at room temperature. During repeated Li stripping/plating cycles, the enhanced bulk Li diffusion kinetics maintain the close interfacial contact, leading to excellent long‐term cycling stability for over 4000 h with a high cumulative areal capacity. These findings provide valuable insights that promoted mass transport in lithium metal anode is of great benefit to high‐performance solid‐state lithium metal batteries.